A new piece of custom malware sold on the underground Internet market is being used to siphon payment card data from point-of-sale (POS) systems, according to security researchers from antivirus vendor McAfee.

Dubbed vSkimmer, the Trojan-like malware is designed to infect Windows-based computers that have payment card readers attached to them, McAfee security researcher Chintan Shah said Thursday in a blog post.

The malware was first detected by McAfee's sensor network on Feb. 13 and is currently being advertised on cybercriminal forums as being better than Dexter, a different POS malware program that was discovered back in December.

Once installed on a computer, vSkimmer gathers information about the OS, including its version, unique GUID identifier, default language, hostname, and active username. This information is sent back to the control and command server in encoded format as part of all HTTP requests and is used by the attackers to keep track of individually infected machines. The malware waits for the server to respond with a "dlx" (download and execute) or "upd" (update) command.

VSkimmer searches the memory of all processes running on the infected computer, except for those hardcoded in a whitelist, for information that matches a specific pattern. This process is designed to find and extract card Track 2 data from the memory of the process associated with the credit card reader.

Track 2 data is information stored on the magnetic strip of a payment card and can be used to clone the card, unless the payment card uses the EMV (chip and pin) standard. That said, in an announcement posted earlier this month on a cybercriminal forum, the malware's author said that work is being done to add support for EMV cards and that "2013 will be a hot year."

The malware also provides an offline data extraction mechanism. When an Internet connection is not available, vSkimmer waits for a USB device with the volume name KARTOXA007 to be connected to the infected computer and then copies a log file with the captured data to it, Shah said.

This suggests that vSkimmer was designed to also support payment card fraud operations that benefit from insider help in addition to remote thefts.

VSkimmer is another example of how financial fraud is evolving and how banking Trojan programs are moving from targeting the computers of individual online banking users to targeting payment card terminals, Shah said.